Once in six lifetimes every day.

I remember when I was in elementary school, and I heard on the radio that the solar eclipse that was about to happen was the last one that would be visible in the Northern Hemisphere for some impossible number of years. This was very depressing to me since our family hadn't had a chance to go to the planetarium to buy some of those glasses that you use to watch an eclipse. I was forced to do that thing where you punch a hole in a sheet of paper and let the hole act as a sort of lens to project an image of the sun onto another surface. This was not very satisfying, but the alternative was to watch it with my naked eyes and burn blind spots into my retina.

We also had a book about Halley's Comet, and I think it was called Halley's Comet And You. (A quick internet search reveals that the book has probably been out of print for twenty years. I can't find mention of it ever existing.) It told me that Halley's Comet will not be visible again until I am in my seventies. I hope I don't fall asleep early that night, because I will be about 150 years old by the time I have another chance to see it. (It also told me the circumference of the comet's orbit, as measured in hot dogs placed end-to-end.)

Halley's Comet and You included a picture of this tapestry, which depicts an appearance of Halley's Comet.
"Wow! Someone better go tell Harold about this."

Luckily, comets seem to be more abundant than I was led to believe by Halley's Comet and You. Two visible comets (Hyukatake and Hale-Bopp) appeared in 1996. Suddenly the universe was lousy with them! I got up in the middle of the night a few time to look at Hyukatake. Hale-Bopp was cool too, but not as impressive. It should have waited another century or so.

Then there was that comet that ran into Jupiter with the force of some huge number of atomic bombs. I'm not sure what that means for a gas giant -- shouldn't it just sort of pass through?
(Edit: Ari tells me that all gas giants have a rocky core. They think so anyway.)

Now I just found out today that there will be a transit of Venus (a very very partial eclipse of the sun by the planet Venus) next year, and the next one won't occur for 104 more years. There is no way I will remember to look for it by then!


Here is what I'm getting at: These things are all incredibly rare events. At the same time, it seems that for astronomers, incredibly rare events happen all the time. I wonder how many once-in-lifetime spectacles I have missed in my life already. Not to worry; there will probably be another soon.